N-acetyl-p-aminophenol has proved beneficial in medical practice due to its analgesic action. However, this compound is not exempt from certain toxic effects in high doses, in particular hepatotoxicity.
Certain compounds resulting from the combination of p-aminophenol and various amino acids, in particular compounds having the formula I in which the symbol R represents a hydrogen atom, have been found to possess useful analgesic properties in therapeutic doses. They alleviate various types of pain. The most active representatives of these new products possess qualities superior to those of the reference product (N-acetyl-p-aminophenol): they are less toxic and the difference between therapeutic doses and those which provoke undesirable side effects is greater; in addition, they are highly soluble in water and may be used in injectable galenic forms, which is not the case for N-acetyl-p-aminophenol.
Furthermore, it is well known that certain organic acids such as acetylsalicylic acid, 5-(2,4-difluorophenyl)-acetylsalicylic acid, 1-(p-chlorobenzol)-5-methoxyindoleacetic acid, certain arylpropionic acids and certain anilinophenylcarboxylic or acetic acids are used in human medicine as non-steroidal anti-inflammatory agents and analgesics.
Nevertheless, the use of these acids is generally accompanied by various types of gastro-intestinal disorder, inparticular hemorrhages and ulcers.
Surprisingly, it has been found that compounds of formula I in which the symbol R represents an acyl radical derived from organic acids such as those defined hereinabove are highly active biological compounds and that, in comparison with the parent acids, the most interesting members of the series are appreciably less toxic, less harmful and less ulcerigenic, while still possessing remarkable efficacy and a more favourable therapeutic index.